1. Field of the Invention
The present invention relates to a semiconductor integrated circuit. Particularly, the present invention is directed to a semiconductor integrated circuit provided with an input circuit device which can detect a level of an input signal having a range narrower than the power supply voltage.
2. Description of the Related Art
In a semiconductor integrated circuit, an input signal having an input level having a range narrower than the power supply voltage of the circuit (for example, when the power supply voltage is 10 V, the input signal has a level of 5 V) is often applied to its input circuit.
In some cases, the semiconductor integrated circuit will have a power supply voltage of a predetermined value (for example, 10 V), and the output signal of a prior art semiconductor integrated circuit having a power supply source lower in value (for example, 5 V) will be input thereto. In other cases, the semiconductor integrated circuit may be a special one (for example, a metal-oxide semiconductor (MOS) circuit) and the output signal of a prior art semiconductor integrated circuit (for example, a transistor-transistor logic (TTL) with a different logic amplitude will be input thereto. In such cases, the latter semiconductor integrated circuit recieves an input signal with an input level having a range narrower than the power supply voltage, as mentioned above.
The input circuit of such a semiconductor integrated circuit can consist of an inverter circuit including a pair of transistors. That is, the inverter includes a P channel transistor and N channel transistor, each having a gate connected to an input terminal.
In such an input circuit, as explained in detail hereinafter, both the P channel transistor and N channel transistor in the input circuit may be ON at the same time, resulting in consumption of a large amount of power, and reducing the inverting speed. Further, there is the problem of only the N channel transistor being switched on and off along with variations in the input signal, whereupon the output obtained from the output terminal OUT becomes insufficient to perform a level change operation.